As a way to overcome the limitation of thermal resistance and chemical stability of polymer, recently, technical development of a ceramic heat generator of high-performance and new function has been actively conducted. This heat generator is prepared in the form of paste including mainly silver (Ag)-based, palladium (Pd)-based or ruthenium (Ru)-based oxides, and among these, silver itself is difficult to be used as heat generating resistor, since it is a conductive material having low resistance, and has a positive temperature coefficient of resistance. Therefore, in order to compensate for this, palladium and ruthenium are added to the ceramic paste. However, since ruthenium has specific resistance higher than silver, an added amount thereof is eventually larger in order to have a lower resistance value. Further, as the added amount of ruthenium is increased, the resistance of paste itself is increased, and thus, temperature is raised with increasing resistance, and eventually power consumption is increased.
Due to the disadvantages of the metal oxides, a way to use carbon, metal coating powder or a mixture thereof, a carbon nanotube, or the like as alternative materials has been reviewed.
As the related art of carbon materials, there are a heating seat manufactured using a fiber heat generator of carbon materials, such as in Korean Patent Laid-Open Publication No. 10-2012-0000878, a technique to prepare a liquid-phase exothermic composition and coat it to a sheet such as in Korean Patent Registration No. 10-1029147, a heating material further including a heating layer consisting of carbon materials in a base materials such as cotton, non-woven fabric such as in Korean Patent Laid-Open Publication No. 10-2010-0053434, or the like.
Among these, the fiber heat generator has difficulty in being processed in a fibrous form due to low elongation, and has high modulus of elasticity so that it is easily ruptured. Further, in the case that the exothermic composition is prepared and coated on a sheet, or a heating layer is further provided on a base layer, the heat generating layer or coating film is released under a high temperature environment of 300° C. or more, or the coating film is easily broken.
In order to overcome those disadvantages, there is a technique to add a ceramic binder to carbon materials, however, the carbon materials added to a ceramic binder is difficult to be mixed due to high oil absorption and hard workability, and thus, it is almost impossible to add 50 wt % or more of the carbon materials. If the content of the binder is increased in order to compensate for this, physical properties and workability will be improved, but conductivity will be lowered.
Accordingly, there is demand to develop a paste composition having high thermal resistance, while having high heat generating efficiency without changing physical properties by overcoming these disadvantages.